How much would it cost to get a return train from London to Reading?

I might have to go for an interview, thanks
Between £17.70 and £85.00 - depending on which route you wish to take (from Paddington or Waterloo), the time you want to travel (it is cheaper outside the rush hour with an off peak ticket) and whether you go 1st or 2nd class. Those are the prices if you have no railcards which give you a reduction in the fare (student, senior, family, military, etc).
Why don't you check the train line companies instead of asking here? God....
Off Peak Return from London Paddington to Reading £22.50. (£42.50 before 09-30am weekdays) Make sure you catch a fast service first or second stop Reading. Takes less than 30 minutes. Christophers £85 is a First Class Peak hour return www.nationalrail.co.uk (site down at the time of answering) www.firstgreatwestern.co.uk www.railcard.co.uk